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« Last post by artbyrobot1 on January 03, 2025, 12:40:44 AM »
I've had an epiphany. So in the winch in place pulley system I was working on before, my concern was that when winching in the string things would be taught and reliable but when the motor reverses and releases string, that is when any snags in the system could cause the string to not be taken up rigidly and tension on the system is then lost and the motor is then unspooling string which isn't being taken up which will result in a spaghetti mess of string spraying everywhere out of control and getting all tangled up. The solution I had was a constant tension spring attached to the turn in place pulley output that would ensure that always keeps the string in tension as the motor unwinds. However, that was a extra cost and complexity and volume taken up by yet another thing and when you multiply that out by 300+ motors that's a LOT of springs added taking up a ton of extra space. That is why I moved to a belt based system instead of string and winch based for the first pulley. So the epiphany was this: it hit me that I can simply have the spring that does the extension of the final finger joint be what puts tension on the whole system and then if at any point in the system a snag were to happen, rather than tension being lost as the motor blindly unravels, not detecting the snag, I could have the motor NOT actively unwind anything at any point! So the motor, when unwinding is to occur, will simply turn OFF, rather than actively drive the unwinding electronically. It can pulse width turn off just acting as a brake to moderate speed of extension but at no point do any counter clockwise release or unwinding of the string. This way, the system only itself pulls string off the motor output shaft and if the system at any point snags, the extension stops and the string is all still under moderate tension but just no further advancement takes place and the motor does nothing further but blindly turning on and off but not actually spraying out thread everywhere at all. Eventually, the potentiometer measuring the joint angle of the finger joint would detect things are not moving and the system would KNOW it has a snag somewhere and at that point it would perhaps try to contract then attempt extension again hoping to dislodge the snag. If this did not work, the system would go into a troubleshooting routine like notifying the user (myself) to fix it or fixing it itself or w/e. But no damage would occur in this setup involving a unraveling mess or tangled mess. Simply the snag itself would be discovered and addressed but no catastrophic series of failures would result in theory under this new setup.
So with all of that said, and this solution in place, I am ready to return to the turn in place style winch style first pulley setup I had before and then the Archimedes pulley will do the rest. So the first pulley will be 2:1 downgearing and the Archimedes system will do 16:1 for a total of 32:1 downgearing. No constant tension spring needed anymore! Much simpler now. Everything I was concerned about is then solved now.
The belt based system fix ideas I was going for may have worked but as of right now I'm abandoning that course. I prefer the winch style and think belts would be higher maintenance and slippage would perhaps be an issue even with all the changes I had mentioned to improve on it. The fact is, belts only have so much surface area to grip onto so they don't scale down too well to tiny pulleys IMO. Large pulleys are better due to large surface area and more for the belt to grip. So my super miniature belt idea was a bit doomed from the start even if it could have worked (and it may well have worked) it just isn't ideal theoretically and I'd rather go with something I trust more intuitively for now.
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So me a bit later...
you can actually get a robot to stand. with a pitch joint, you know the direction!!! towards the ground and away from the ground.
So if u keep pushing down till the accellerometre tilts away from the leg, you know youve hit the ground.
Then if u do it with all 4 legs, wait for the right elevation and centre angle, and u know if u need to push down, or stop pushing down!
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« Last post by artbyrobot1 on December 14, 2024, 03:11:19 AM »
Ok so my belt drive system from my last update just is not quite up to par in terms of grip and anti-slippage. So my new series of changes are planned out and underway now. First, I will be bumping up the height of each pulley to 2mm up from 1.1mm. This will double the surface contact area for way more belt grip in and of itself. So then I can use a 2mm wide belt. Next, I'll be increasing the drive pulley diameter to 1.5-2mm additional diameter. This will also greatly increase surface contact with the belt for more grip. Then finally, I'll be using a commercial belt that is said to have the highest grip of all belts - its called a polyurethane belt. It is a flat belt with 2mm width and .9mm thickness. It should be a huge upgrade to my current setup! Here's some photos of it:   The best part is you can customize the diameter of the belt by melting the two ends together! This was a key thing I did not know! So I can create just the right size and it should be perfect! I can also double these up by melting two belts layer by laer for a 1.8mm thick square shaped belt that is even less stretchy and so can be even more able to tightly grip my pulleys. I'm very excited about this and think it will take us to where we need to be *crossing fingers*.
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Making encoders is a bitch, and dc motors are cheaper without them. So it would be cool if u could get a robot to work without them. Its a seemingly impossible thing, cause a legged robot cant even have a centre point for its motors to even just stand still! If you put mechanical end stops, then you can at least know the end point positions, that could help. If you dont have positional information, the trick is maybe u could correllate it from accellerometre information over time, so you exchange the positional information for so many accellerometre samples and maybe its equivilent information! So u just need to correllate it, with machine learning. Its actually a little of a long story to explain it, but I think its possible! U just need to get in the right semantical/generation space to make it happen. So if you take it from the position of searching inside of a physics engine (as the generation space), you predict the next accellerometre accelleration, from a chain of accellerometre data, and u step it each new frame, and the chain of accellerometre data is replacing the lack of angular position information, but it should be equivilent. Then that should build the virtual copy of the physics, which lets u then brute force the robots motor commands to get the robot in action, WITHOUT encoders! 
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I've been wanting to put a robo together for years now, but I'm really sick from smoking cigarettes so I still haven't got it finished. I've got a really cool innovation I want to share with you guys about getting rid of the motor encoders and how it shouldn't matter, robots dont actually need them!!! I'll bring it up sometime here in the near future. This is work over the last couple of years-> Heres a virtual sim of my bot going (I paid a bit of attention to the look of the graphics.) But the main thing is the physics being correct, and its a bit dodgy still, the robot is just moving with random motions. The end product would be the two robots having a fight on screen, in a virtual environment. https://www.youtube.com/watch?v=XdIJCjYODZwHeres another one with the graphics taken off, of the two robots upside randomly moving. https://www.youtube.com/watch?v=coJcZKJNLKQ(Computer vision) heres a stereo rgb -> depth map on the gpu. (ran pretty bad, theres alot of matches to do!) https://www.youtube.com/watch?v=deRUU9j-uTUHeres a little robot kit i put together and got some random movements out of it-> https://www.youtube.com/watch?v=LJfyyzP7ec8https://www.youtube.com/watch?v=Hw6Q9GOrRnkhttps://www.youtube.com/watch?v=wmVr-beVAJYhttps://www.youtube.com/watch?v=GJaMAWIcH-c
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« Last post by artbyrobot1 on November 22, 2024, 04:32:23 PM »
Ok so I was struggling to plan out how the flat spiral coil constant force spring would maintain constant tension on my first winch in place pulley the past couple days and I was studying how tape measures use these springs. Then it hit me when a colleague was mentioning belt pulley based downgearing that a belt pulley based downgearing for this first pulley would remove all the issues of derailment and need for constant tension during whole duration of travel a winch style would require in this design. Also, since its just .4lb-.8lb of force for the first pulley downgear, as long as the belt is reasonably tensioned and has some decent grip to it, I should not deal with a ton of slippage issues and the motor's output should be passed along well. So here is my beginning attempt at converting my first pulley to a belt based pulley instead of fishing line winch based pulley.  This is made just using adhesive transfer tape applied to one side of a nitrile glove and cut out into a 1.1mm wide strip and applied to the two pulleys directly. Built in place. Early testing shows it needs more layers to have less stretchiness or needs to be reinforced internally with fishing line wraps between layers to prevent so much stretch to it which causes slippage. Also, the motor output shaft acting as the winch pulley is a combination of a bit too small in diameter and a bit too smooth to create a proper grip. So I'm thinking of thickening it up some and adding a grippy surface to it so that it grips the belt better with less slippage. I am considering using silicone rubber to coat the motor output shaft or several wraps of nylon upholstery thread and super glue to thicken it then coating that with carpet anti-slip paint. Or silicone. I'm considering making the belt from a cloth coated in silicone or carpet anti-slip paint and then sewn tightly into place over the pulleys - creating a sewn seam for a tight grip. I'm considering a tensioner pulley but I think that's overkill and should be avoided unless it proves absolutely necessary. I have not explored purchasing options at this time but of course I'm open to look into this in the future. The thing about a premade is it would have to be a perfect fit in both length and width and I'm not sure if that will be easy to find or not. This is all a very new approach so I can investigate that later. For now I'm happy to just move quickly on the prototyping with materials on hand.
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I see there are many local competitions. I hope you find a suitable group soon.
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« Last post by endinvest on November 10, 2024, 08:50:07 PM »
Hello,
I'm also new, glad if I can connect with your project.
Could you provide some more information about it?
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« Last post by artbyrobot1 on November 08, 2024, 12:48:37 AM »
I just ran a test of the second turn in place winching pulley and ran into several problems. First I noticed my main lines turning the motor were not the full 27"+ which I thought they were but just remeasured and found they weren't. My bad. So I have to rewind those to fix that. Next, I noticed that just as we depart from the motor output shaft we experience mechanical advantage with each downgearing, so also when traveling from the downgeared area back to the motor output shaft we experience mechanical disadvantage. Up-gearing. Which means the bolt hanging as a load to place tension on the pulleys during a release cycle was not enough weight anymore (was barely enough before now clearly not enough). Now note that the bolt represents what a tension spring will normally be doing, tensing up the winch system to keep it all solid and tight. I don't want this to have to be much heavier than the bolt. I want the system to not need much pulling to remain good in tension. The friction of the teflon tubing plus mechanical disadvantage etc was causing the pulleys to not remain tense (and their not being lubed yet on the junction between fishing crimp sleeve and thumb tack. So my solution I'm now contemplating is either moving one of the turn in place winches down to the location of the Archimedes pulleys on the forearm area and putting the tensioner apparatus between it and the previous pulley mounted on the motor so that the tensioner apparatus does not suffer as much mechanical disadvantage due to up-gearing OR I get rid of the second pulley entirely and just have the winch in place be a single pulley 2:1 and the Archimedes system be 16:1. Which still works as we have then 32:1 which is great still. Under such a system, the original 27" winching would be reduced to 13.5" by the winch in place pulley attached to the motor. The Archimedes pulley system then needs to go down, around one pulley, back up, around another pulley, then down and around another pulley, then back up and tie off. The total travel for those one down, one up, one down, one up (4 trips) is 13.5/4 so 3.4". And we'd sit at 8:1 at that point. so adding two more pulleys beneath that first group would add another 4:1 for 32:1 total. And those two pulleys would add another half inch tops so that gives us around 4" total length of the Archimedes system and not too crazy many turns in that first system like we had in our first prototype. Still quite simplified comparatively speaking. So this is a very viable solution. And that 4" is around 10cm and we had 11cm already planned for this purpose in the CAD in the forearm from before. So we are still within that target and viable still without any change to the CAD at all which is great. Anyways, back to the test's issues discovered. Oh yeah, also, the load (in this case a bolt hanging) struggled to keep the turn in place winches under tension while the motor was releasing the bolt (loosening or unwinching itself) not only because of the mechanical disadvantage from the pulley upgearing itself and from the friction in the TPFE guidance tubing but also from the friction of yet another pulley and its friction between its fishing crimp sleeve and its thumbtack. So I was having to manually pull down assisting the bolt, pulling down fairly hard just to get the system to stay taught and release without becoming a derailed tangled mess. One other work around if I were insistent on going with more than one winch in place pulley would be to wind up extra line onto each turn in place winch pulley and have that directly attached to a tensioner spring placed wherever on the robot. This would always keep tension on just that winch in place pulley and be responsible for just that pulley and suffer no mechanical disadvantage beyond the TPFE guidance tubing it has to pass through to get there which shouldn't be too bad if the spring can be nearby. This is a valid solution but adds another layer of complexity to the winch in place pulleys and now more routing and string to deal with. It also means loads of extra springs to place. Attached is a drawing of the proposed tensioning mechanism for tensioning each pulley individually.  In any case, were I to add this type of tensioning apparatus to each pulley and the necessary extra plastic disc and vertical spacing to glue string to the fishing crimp sleeve and wrap it up, that takes up even more vertical space in the system and we were already really lacking sufficient space as is. So to gain the extra space needed to do that, we'd have to extend the height of the fishing crimp sleeve to accommodate this which would then remove the option to add the reverse direction set of pulleys to the same thumb tack. Although that is probably fine now that we were planning to achieve that with just a tension spring as the actuator for extension of fingers instead of motor actuated extension and coupling that with a n20 gear motor for extra oomph in demand on a rare as needed basis for extension action when the tension spring is not strong enough to do it for the task at hand (rare). So yeah, this apparatus would work to solve the issues I'm having with my current test setup I think. But just going 16:1 on the Archimedes instead of 8:1 on the Archimedes pulleys and simply deleting the second winch in place pulley on the motor seems like the best option to me right now. Doing so means the Archimedes pulleys bumps up from 27/4 = 6.75" for Archimedes pulleys to deal with 6.75/4 (for up and down passes around first group of pulleys) so 1.68" in length then another pulley brings it to 2.1" total length compared to 27/2 (only one winch in place pulley) = 13.5" for Archimedes pulleys to deal with 13.5/4 (for up and down passes around first group of pulleys) so 3.4" then add 2 more pulleys so 4.2". So 2.1" vs 4.2". If we keep the second winch in place pulley we shave off 2.1" in Archimedes pulley system total length and shave off one pulley from its system too. Well I think just going 16:1 on the Archimedes is my move here. The winch in place pulleys have been a finicky mess to me. I prefer the Archimedes style pulley more and prefer to have that do the lions share of the downgearing after that first winch in place pulley cuts our total run-out in half. It still is a very useful help to cut things in half like that and much appreciated. But any more winch in place action is asking for trouble. I am much less able to control it and prevent issues that I feel I can do with the Archimedes pulley system. And you all have not seen my Archimedes pulley system in action it is really beautiful and elegant to watch and totally silent. So I'll rely on it more and keep the winching turn in place pulleys to the minimum 2:1. Someone trying to do their own robot may appreciate that I'm leaving these options for further exploration open for future devs. I'm going the way I am most comfortable but if you think the winching method is more comfy for you, downgear more with those than I chose. I am not ruling that out here - just preferring the Archimedes more based on my experiences so far.
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« Last post by artbyrobot1 on November 07, 2024, 12:49:28 AM »
I have added the final pulley and rigged the guidance TPFE tube up to that pulley and routed that to the general vicinity of the Archimedes pulley downgearing system. As seen in the photo, I used super glue and post it note paper to form a TPFE guidance tube support structure to hold it in place as well as wrapped it in fabric tape and soaked that tape in super glue. I applied the super glue with the tip of a sewing needle as a precision application method.  The next step will be to test the pulley system as is and make sure everything is working really well. If all testing passes, we will then modify the Archimedes pulley system on the forearm that we were using before to simplify it some since it now deals with only 7" or so of string compared to 27" of string it dealt with when we did not have the turn in place pulley system in place. So it will now be much more compact and fewer pulleys needed in it. So a bit of redesign and part recycling and we'll be good to go on that. Also, before, it was a 16:1 Archimedes pulley system whereas now it will just be a 8:1 system.
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